You can just jumper the green wire to a black one on the PSU connector and the fan will spin up and the supply produce voltage. So the answer is yes.
Minimum you need is to connect the PSU to the MB and the case switch to the MB pins (PSU needs to see a momentary connection on those pins to start up).
If the PSU fan spins up I then connect the keydb, mouse, case speaker, RAM and CPU to see if I get just the single post beep. If that works Video card follows.
Once I see the VGA boot screen I know I have a good computer and can install HD, CD/DVD sound etc. with no fear.
This can all be done with the MB out of the case laying on a non-metalic surface.